1. Field of Invention
a. The present invention relates to method and apparatuses for treating persons with visual mid-line shift syndrome, vertigo, dizziness and spatial dysfunction causing difficulty with mobility, ambulation and driving of an automobile.
2. Introduction
Persons incurring neurologic events such as a traumatic brain injury (TBI) or Cerebrovascular accident (CVA) can result in visual field loss. The field loss will often be projected to the same field of view for each eye. This means that a neurological event affecting the right cerebral cortex will cause a field loss in the left field of both eyes. This is termed a left homonymous hemianopsia. A lesion affecting the left cerebral cortex will produce a field loss for each eye on the right side. This is termed a right homonymous hemianopsia.
This type of vision impairment will cause significant interference in function and performance. Homonymous hemianopsias will directly affect spatial orientation, posture and balance. Persons with this resultant condition will frequently bump into objects on one side and are more susceptible to injury from trauma or falls. This is due to the homonymous hemianopsia causing a Visual Midline Shift Syndrome (VMSS) which affects the concept of the ego center or visual midline in addition to the blind spot produced by the field loss. Also, it causes reading to become very difficult because right homonymous hemianopsia causes a spatial visual field loss which blocks the next word to be read. Consequently, a left homonymous hemianopsia causes difficulty in shifting gaze from the end of the line of print on the right side to the beginning of the next line of print.
In addition, homonymous hemianopsia interferes with daily living skills. Activities such as shopping in a store, conversing in a group of people, and even finding food on the plate will become very challenging. In turn, homonymous hemianopsia will affect socialization and reduce independence. A person with a homonymous hemianopsia is most often not safe to drive. This will in turn affect employment, earning potential, family relationships, to name several.
Homonymous hemianopsia can be determined behaviorally as well as clinically. Behaviorally, a person with a homonymous hemianopsia will have spatial difficulties causing bumping into objects, drifting when walking and/or not seeing objects on the side of the field loss. Clinically doctors will perform a visual field test to diagnose the condition. There are many different types of manual as well as automated visual field tests that require a response from the patient. All tests utilize a monocular assessment and require that the patient hold his or her fixation steady on a target. The standard automated instrument then projects sequential isolated lights that are timed to be presented in the peripheral field of the patient. The patient then presses a button each time he/she sees the light. The instrument then maps the visual field and corresponding field loss for each eye.
Research has shown that the visual system is composed of at least two processes. The focal visual process is primarily a function of the occipital cortex is oriented towards details related to higher cognitive process for attention. The second process is ambient and spatial in nature. Rather than being central in origin, it is mediated by the peripheral section and information is relayed through axons to the mid brain. It is here that information about a potential context (vertical and horizontal lines and boundaries in the peripheral field as well as orientation of the plane of the floor) is matched with sensory-motor information from the kinesthetic, proprioceptive and vestibular systems for organization of balance, posture and movements. This process organizes this information much faster than the focal process and before the detail is deceived the ambient process feed-forwards spatial information to 99% of the cortex willing the occipital cortex where the focal visual process functions.
Following a neurological event such as a TBI, CVA, etc. dysfunction can occur interfering with the ambient spatial visual process. This leaves the focal visual process to isolate on detail without the spatial context from the ambient system. In turn, the affected focal visual process attempts to function, but it lacks the ability to adapt to changes and becomes bound on details.
It is the ambient visual process that releases the focal process form isolation. Also, the ambient visual process is continually anticipating change and acts as a balance against isolation or over-focalization on detail. Dysfunction between these processes causes slow reaction time and an inability to adapt to environmental changes. This condition has been called Post Trauma Vascular Syndrome (PTVS).